This is a response signal to the STROBE, PRG_RST, 
STEP_RST, CYC_RST and DO_RST signals.    When one of 
these signals is input, the ACK signal is sent back to inform 
that appropriate processing has finished. 
This signal can always be used, irrespective of the master 
mode selected by means of the MODE switch. 
If two (2) or more input signals shown above are input at the 
same time, only the signal which was input first is processed, 
then the ACK signal is output.